From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753279Ab3GHVoJ (ORCPT ); Mon, 8 Jul 2013 17:44:09 -0400 Received: from mga14.intel.com ([143.182.124.37]:2182 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751026Ab3GHVoG (ORCPT ); Mon, 8 Jul 2013 17:44:06 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,1022,1363158000"; d="scan'208";a="328410507" Subject: [PATCH] x86: perf: fix incorrect use of do_div() in nmi warning To: linux-kernel@vger.kernel.org Cc: x86@kernel.org, Dave Hansen From: Dave Hansen Date: Mon, 08 Jul 2013 14:44:04 -0700 Message-Id: <20130708214404.B0B6EA66@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen This fixes a bug present in 3.10 and introduced here: commit 2ab00456ea8a0d79acb1390659b98416111880b2 Author: Dave Hansen Date: Fri Jun 21 08:51:35 2013 -0700 x86: Warn when NMI handlers take large amounts of time I completely botched understanding the calling conventions of do_div(). I assumed that do_div() returned the result instead of realizing that it modifies its argument and returns a remainder. The side-effect from this would be bogus numbers for the "msecs" value in the warning messages: INFO: NMI handler (perf_event_nmi_handler) took too long to run: 0.114 msecs Note, there was a second fix posted by Stephane Eranian for a separate patch which I also botched: http://lkml.kernel.org/r/20130704223010.GA30625@quad Both of these fixes need to get pulled in to Linus's tree and the 3.10 stable tree. Signed-off-by: Dave Hansen Cc: stable@vger.kernel.org Cc: x86@kernel.org --- linux.git-davehans/arch/x86/kernel/nmi.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff -puN arch/x86/kernel/nmi.c~dave-is-stupid-do_div arch/x86/kernel/nmi.c --- linux.git/arch/x86/kernel/nmi.c~dave-is-stupid-do_div 2013-07-08 13:10:55.498656504 -0700 +++ linux.git-davehans/arch/x86/kernel/nmi.c 2013-07-08 13:10:55.501656637 -0700 @@ -111,7 +111,7 @@ static int __kprobes nmi_handle(unsigned */ list_for_each_entry_rcu(a, &desc->head, list) { u64 before, delta, whole_msecs; - int decimal_msecs, thishandled; + int remainder_ns, decimal_msecs, thishandled; before = local_clock(); thishandled = a->handler(type, regs); @@ -123,8 +123,9 @@ static int __kprobes nmi_handle(unsigned continue; nmi_longest_ns = delta; - whole_msecs = do_div(delta, (1000 * 1000)); - decimal_msecs = do_div(delta, 1000) % 1000; + whole_msecs = delta; + remainder_ns = do_div(whole_msecs, (1000 * 1000)); + decimal_msecs = remainder_ns / 1000; printk_ratelimited(KERN_INFO "INFO: NMI handler (%ps) took too long to run: " "%lld.%03d msecs\n", a->handler, whole_msecs, _